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Questions answered during the expedition are below.


Question:
I am familiar with bioerosion in corals, coral rubble, and coral reef carbonate substrate in shallow water. Bioerosion is done by small invertebrates of several taxa boring into carbonate substrate. Small animals (cryptofauna) of many taxa live in holes formed by bioerosion.

Do bioerosion and cryptofauna exist in deepwater corals? If so, it would be useful to study them. For example, what would be the relationship between the taxa from deepwater coral sediments on platforms and any cryptofauna living within bioeroded spaces in the coral skeletons? And what would be the impact of bioerosion as a constraint to hard coral growth?

~ Dave Moran
Bureau of Ocean Energy Management (BOEM)



Answer:
This question has been looked at elsewhere, but not specifically in the Gulf of Mexico. Previous work on Lophelia pertusa in the Northern Atlantic has shown that there are a number of organisms, most prominently boring sponges (eg. Spiroxya heteroclita) and endolithic fungi, that actively erode skeletal material. In addition, there are a number of taxa that encrust the skeleton including hydrozoans, serpulids, bryozoans, bivalves, actinians, and stylasterids. These encrusting invertebrates seem to build up reef structure, either by directly contributing material or increasing sediment trapping, rather than actively eroding skeletal material. Interestingly, the symbiosis between Lophelia pertusa and the polychaete worm Eunice norvegica also strengthens skeletal structures by creating tubes that connect skeletal fragments, resulting in higher rates of reef accretion.

In general, it appears that bioeroders and encrusters only colonize dead skeletal material and that live tissue prevents colonization. So, I would expect that bioerosion is not a major constraint on growth, but that it almost certainly leads to degradation of reef structure as a whole over time. This is an interesting question however, and probably warrants further investigation, especially in Gulf of Mexico populations, as well as with non-scleractinian cold-water corals.

~ Sam Georgian   PhD student, Temple University

 

 

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